The present invention relates to methods of preparing an article including a superhard component such as diamond or borazone and a metalloceramic matrix material.
Known in the prior art are methods of preparing articles from a superhard diamond-containing material by hot pressing thereof.
In accordance with these methods, it is necessary to prepare special graphite press-moulds which are generally used only once. The articles after sintering are covered with graphite and, hence require additional treatment. A great disadvantage of these prior art methods resides in the fact that the articles become saturated with carbon contained in the press-mould, which is in many cases impermissible.
Widely known is a method of "free sintering" of metalloceramic articles, which method is free of the aforementioned disadvantage, since the application of a graphite press-mould is not necessary. The articles have a high quality surface finish, thus making it possible to use these articles for tooling without any additional processing.
The foregoing method of free sintering, however, is practically unacceptable for preparing diamond-containing articles due to the fact that in the course of shrinkage of the powdered matrix material around the incompressible diamond grains, cracking of the sintered composition takes place.
By the term "free sintering" we mean the process of shrinkage of a metalloceramic article which occurs as a result of heating the article formed from a powdered material and disposed in free conditions without any press-mould, i.e., the pressed article is disposed on a fire-proof base or a refractory powder layer such as for instance, alumina.
Thus, during such a sintering process the article is not subjected to any external loads which usually result from the mechanical action of the press upon the plunger of the press-mould, as in the case of hot "non-free" pressing.